The present invention is related to an apparatus for monitoring the rotational speed in a wind energy plant. Such an apparatus is sometimes also called a rotational speed monitor.
The drive train of a wind energy plant begins with a rotor which carries the rotor blades. The rotor is connected to a rotor shaft, which is coupled to a gearbox. The rotor shaft is sometimes also called a slow shaft. The output shaft of the gearbox runs out into the generator as the generator shaft and is also called the rapid shaft. In known wind energy plants, a toothed disk is arranged on the rotor shaft, which generates pulses via inductive pulse transmitters, the frequency of which is proportional to the rotational speed of the rotor shaft. The pulses are analysed by an electronic module. Also, the sampled pulses are converted into a current signal via a frequency/current converter (f-I converter) and reach a central control unit of the wind energy plant. In the central control unit of the wind energy plant, a critical cut-off rotational speed is filed. When the rotational speed values of the rotor shaft are above the filed cut-off rotational speed, controlled setback of the wind energy plant takes place.
It has proven to be a drawback of the apparatus for monitoring the rotational speed that the rotational speed monitoring does not have sufficient functional security, in particular, it does not comply with a safety integrity level which is required for security directed implementations according to IEC 61508.
The present invention is based on the objective to provide an apparatus for monitoring the rotational speed which provides sufficient functional security for the implementation in a wind energy plant with means which are as simple as possible.